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At least 19 recordsLinked to original sources
PubMed1992

Midline and lateral field sound localization in the ferret (Mustela putorius): contribution of the superior olivary complex.

1. The ability of ferrets to localize sound in space was determined before and after unilateral or bilateral lesions of the superior olivary complex (SOC). Lesions were made by pressure injection of kainic acid into the SOC through a stereotaxically positioned glass micropipette. The lesions destroyed the cell bodies in the superior olive without disrupting fibers of passage in the trapezoid body or other pathways in the auditory brain stem. The integrity of fibers was demonstrated by protargol staining of axonal processes and by the retrograde transport of horseradish peroxidase (HRP) from the inferior colliculus to other auditory brain stem nuclei. Behavioral tests were carried out separately for sound localization at midline and lateral field positions. Minimum audible angles were determined for single 45-ms noise bursts presented through paired loudspeakers positioned symmetrically around 0, -60, and +60 degrees azimuth. 2. Four ferrets received complete lesions of the left SOC, and two received complete lesions of the right SOC. In general, unilateral destruction of the superior olive resulted in impairments in sound localization in both left and right lateral fields. In some cases, deficits were also apparent on midline. Four additional animals received unilateral lesions that spared cells within the SOC. In most cases, deficits were apparent despite incomplete lesions of the SOC. The pattern of deficits was generally consistent with that found in animals with complete lesions. Most animals had difficulty localizing sounds in the lateral fields. 3. Four animals received bilateral lesions of the SOC. Three had complete or near-complete destruction of the superior olive on one side of the brain with relatively minor damage on the other side. Each of these animals exhibited behavioral deficits that were particularly severe ipsilateral to the more extensively damaged superior olive. One animal with complete bilateral destruction of the SOC was incapable of sound localization, even with 2-s noise bursts. This animal, however, suffered severe motor impairments after surgery that might have contributed to the apparent inability to localize sound. 4. Two animals with kainic acid lesions that caused little or no damage to the SOC were still capable of high levels of performance in tests of sound localization and had no elevation in minimum audible angles. These cases served as controls for the possible effects of nonspecific brain damage and demonstrated that kainic acid injections per se resulted in no obvious deficits in our test situation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Visual factors in sound localization in mammals.

The ability of mammals to localize sound varies widely among species. During the past decade, evidence has accumulated that this variation cannot be accounted for simply on the basis of the availability of the physical cues for locus. Evidence is presented that a major factor in sound localization is the need to direct the field of best vision to a sound source for further scrutiny. Thus, species with broad fields of best vision (such as visual streaks) require less accurate information regarding the location of a sound source than do species with very narrow fields of best vision (such as foveae). To support this suggestion, data are reported for the width of the field of best vision in the form of retinal ganglion cell isodensity contours for thirteen species of mammals. The possible contribution of other factors including binocular fields, visual acuity, and the degree to which a species is predatory in lifestyle, is also examined.

Animals↗
PubMed1992

Hearing and sound localization in blind mole rats (Spalax ehrenbergi).

Two blind mole rats were tested for their ability to detect and localize sound. The results indicate that blind mole rats have severely limited, and probably degenerate, auditory abilities. Although their 60-dB low-frequency hearing limit of 54 Hz is within the range for other rodents, the highest frequency they can hear at a level of 60 dB SPL is only 5.9 kHz, giving them the poorest high-frequency sensitivity yet observed in any mammal. In addition they have poor sensitivity as indicated by the fact that their lowest threshold is only 32 dB SPL (at 1 kHz). Finally, they are unable to localize brief sounds but retain a rudimentary ability to localize sounds of 0.5 s or longer. These results, combined with those of previous studies of subterranean species (i.e., blind mole rats, naked mole rats, and pocket gophers), suggest that poor auditory sensitivity, the loss of high-frequency hearing, and an inability to localize brief sounds is a degenerate state which may be characteristic of subterranean mammals. Thus it appears that an exclusive adaptation to a subterranean lifestyle (where airborne sound propagates poorly and where directional responses are limited by the tunnels) can result in vestigial auditory abilities just as the absence of light results in vestigial vision.

Acoustic Stimulation↗
PubMed1990

Effect of bilateral auditory cortex lesions on sound localization in Japanese macaques.

1. The ability of four Japanese macaques (Macaca fuscata) to localize sound was determined after bilateral ablation of auditory cortex. The animals were given two tests: a "midline" test in which they had to discriminate noise bursts presented from a loudspeaker located to the left from identical noise bursts presented from a loudspeaker located to the right of midline, and a "hemifield" test in which both loudspeakers were located in their right hemifield. 2. Both of the tests were administered by the use of two different behavioral tasks: a conditioned-avoidance task in which the animals were trained to make or break contact with a water spout to indicate the location of a sound source, and a two-choice task that required the animals to walk to the source of the sound. 3. The results of both the conditioned-avoidance and the two-choice tasks demonstrated that the animals were able to perform the midline discrimination although their localization acuity was reduced. However, the animals had great difficulty in learning to walk to the source of a sound in spite of the fact that they had received previous sound-localization training in the conditioned-avoidance task. This difficulty suggested that the monkeys no longer associated the sound with a location in space. 4. The results of both the conditioned-avoidance and the two-choice tasks demonstrated that the animals were unable to discriminate the locus of a sound source when both loudspeakers were located in the same hemifield. 5. Bilateral ablation of auditory cortex results in both sensory and perceptual deficits. The presence of sensory deficits is indicated by the decreased acuity in the left-right discrimination and the inability to discriminate between two loudspeakers located in the same hemifield. The deficit in the perception of the locus of sound is indicated by the difficulty in learning to approach the source of a sound, an ability which normal monkeys exhibit without training. 6. There appear to be species' differences in the effect of auditory cortex lesions on sound localization. Although cortical lesions result in a sound-localization deficit in several species of primates and carnivores, they have little or no effect on rats.

Animals↗
PubMed1990

An in vitro analysis of sound localization mechanisms in the gerbil lateral superior olive.

One way in which animals localize sounds along the horizon is by detecting the level differences at the 2 ears. Neurons in the lateral superior olive (LSO) encode this cue by integrating the synaptic drive from ipsilateral excitatory and contralateral inhibitory connections. This synaptic integration was analyzed in 400-500-microns brain slices through the gerbil superior olive. Intracellular recordings from LSO neurons were obtained during the application of independent or conjoint electrical stimuli to the excitatory afferent and inhibitory afferent pathways. Stimulation of ascending fibers from the ipsilateral cochlear nucleus reliably evoked EPSPs and action potentials. Stimulation of the medial nucleus of the trapezoid body (MNTB) consistently evoked IPSPs. The evoked postsynaptic potentials differed in that IPSPs were 2 times the duration of EPSPs. An electrophysiological estimate of convergence indicated approximately 10 excitatory and 8 inhibitory afferents per LSO neuron. MNTB stimulation suppressed synaptically evoked action potentials. When stimulus amplitude was increased to the excitatory pathway, it was generally found that a greater MNTB stimulus was necessary to suppress the action potential. A similar commensurate rise in ipsilateral and contralateral acoustic stimulation was also found to be necessary to give the same criterion response. These results confirm that the LSO can integrate evoked action potentials and IPSPs to encode interaural level. Increasing stimulus voltage was found to decrease both action potential and IPSP latency, suggesting that intensity information may be encoded with temporal cues in the nervous system. It was also found that an evoked burst of action potentials could be inhibited in such a way as to yield intermediate discharge rates, dependent on contralateral stimulus level. Taken together, these results suggest that certain properties related to level-difference coding may be available for intracellular analysis using the brain-slice preparation. Several temporal characteristics of the synaptic potentials, including latency and duration, may play a critical role in this simple computation.

Acoustic Stimulation↗
PubMed1992

Infants' perception of illusions in sound localization: reaching to sounds in the dark.

Sixteen infants each at 4, 6, and 8 months of age were tested for reaching to sounding toys in the dark under two auditory illusion conditions: the Haas-effect, which creates the illusion of a single lateralized sound based on an interaural intensity difference (the toy was visible and invisible under some test conditions); and the midline illusion, which creates the illusion of a single sound at midline due to an absence of any interaural time or intensity differences (invisible toy condition only). No-sound control trials indicated the level of spontaneous reaching in the dark. Results indicate that by 4 months infants perceive both the Haas-effect and midline illusions. The ability to reach both for invisible and visible sounding objects in the dark was well developed by 4 months of age, although developmental changes in aspects of reaching behavior were observed and, at all ages, object contact was most frequent when visual localization cues accompanied sound localization cues. The incidence of spontaneous reaching in the dark was low and did not vary with age. Theoretical and methodological implications of this research are discussed.

Acoustic Stimulation↗
PubMed1992

Development of sound localization.

Perceptual sound localization is determined from differences in time and loudness of signals arriving separately at bilateral ears, with the time difference being the more important one. The author examined the development of sound lateralization using a self-recording device developed by Sato. It measures the sensitivity of sound lateralization on the basis of time and loudness differences separately. Subjects were 59 children aged 2 to 18 years and 12 adults who were audiologically and neurologically normal. Sound stimulus was 500 Hz continuous band noise. (1) The testable rate was increased in children older than the age of 4, and all children over 7 years of age could be tested. (2) Children over 4 years of age could lateralize sound on the basis of time difference. Sensitivity to time differences improved rapidly, showing a steep curve, in children from the ages of 4 to 6, and then increased slowly until adulthood. (3) Sensitivity to loudness differences increased and standard deviation decreased with age. There is a possibility that children aged 4 can discriminate loudness difference almost as well as adults.

Adolescent↗
PubMed1990

Sensitive and critical periods for visual calibration of sound localization by barn owls.

This study describes developmental changes in the capacity of owls to adjust sound localization in response to chronic prismatic displacement of the visual field and to recover accurate sound localization following the restoration of normal vision. Matched, binocular displacing prisms were mounted over the eyes of 19 barn owls (Tyto alba) beginning at ages ranging from 10 to 272 d. In nearly all cases, the visual field was shifted 23 degrees to the right. Sound localization was assessed on the basis of head orientations to sound sources, measured in a darkened sound chamber with a search coil system. Chronic exposure to a displaced visual field caused the owls to alter sound localization in the direction of the visual field displacement, thereby inducing a sound-localization error. The size of the sound-localization error that resulted depended on the age of the animal when prism experience began. Maximal errors of about 20 degrees were induced only when prism experience began by 21 d of age. As prism experience began at later ages, the magnitude of induced errors decreased. A bird that wore prisms beginning at 102 d of age, altered sound localization by only 6 degrees. An adult owl, when exposed chronically to a displaced visual field, altered sound localization by about 3 degrees. We refer to the early period in life when displaced vision induces exceptionally large sound-localization errors (relative to those induced in the adult) as a sensitive period. The capacity to recover accurate sound localization following restoration of normal vision was tested in 7 owls that had been raised wearing prisms. Four owls that had prisms removed by 182 d of age recovered accurate localization rapidly (over a period of weeks), whereas 3 owls that were older when the prisms were removed did not recover accurate localization when tested for up to 7 months after prism removal. Adjustment of sound localization slowed greatly or ceased at about 200 days of age, referred to here as the critical period for visual calibration of sound localization. Three owls were subjected repetitively to displacement of the visual field. An owl that adjusted sound localization to the left of normal during the sensitive period retained the capacity to adjust again to the left, but not to the right of normal, later in the critical period. The converse was true for an owl that adjusted sound localization to the right of normal during the sensitive period.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Physiological↗
PubMed1990

Two-dimensional sound localization by human listeners.

This study measured the ability of subjects to localize broadband sound sources that varied in both horizontal and vertical location. Brief (150 ms) sounds were presented in a free field, and subjects reported the apparent stimulus location by turning to face the sound source; head orientation was measured electromagnetically. Localization of continuous sounds also was tested to estimate errors in the motor act of orienting with the head. Localization performance was excellent for brief sounds presented in front of the subject. The smallest errors, averaged across subjects, were about 2 degrees and 3.5 degrees in the horizontal and vertical dimensions, respectively. The sizes of errors increased, for more peripheral stimulus locations, to maxima of about 20 degrees. Localization performance was better in the horizontal than in the vertical dimension for stimuli located on or near the frontal midline, but the opposite was true for most stimuli located further peripheral. Front/back confusions occurred in 6% of trials; the characteristics of those responses suggest that subjects derived horizontal localization information principally from interaural difference cues. The generally high level of performance obtained with the head orientation technique argues for its utility in continuing studies of sound localization.

Adult↗
PubMed1991

Sound localization by human listeners.

In keeping with our promise earlier in this review, we summarize here the process by which we believe spatial cues are used for localizing a sound source in a free-field listening situation. We believe it entails two parallel processes: 1. The azimuth of the source is determined using differences in interaural time or interaural intensity, whichever is present. Wightman and colleagues (1989) believe the low-frequency temporal information is dominant if both are present. 2. The elevation of the source is determined from spectral shape cues. The received sound spectrum, as modified by the pinna, is in effect compared with a stored set of directional transfer functions. These are actually the spectra of a nearly flat source heard at various elevations. The elevation that corresponds to the best-matching transfer function is selected as the locus of the sound. Pinnae are similar enough between people that certain general rules (e.g. Blauert's boosted bands or Butler's covert peaks) can describe this process. Head motion is probably not a critical part of the localization process, except in cases where time permits a very detailed assessment of location, in which case one tries to localize the source by turning the head toward the putative location. Sound localization is only moderately more precise when the listener points directly toward the source. The process is not analogous to localizing a visual source on the fovea of the retina. Thus, head motion provides only a moderate increase in localization accuracy. Finally, current evidence does not support the view that auditory motion perception is anything more than detection of changes in static location over time.

Attention↗
PubMed1990

Effects of aging on the precedence effect in sound localization.

The precedence effect in sound localization can be evoked by presenting identical sounds (e.g., clicks) from pairs of loudspeakers placed on opposite sides of a subject's head. With appropriate inter-loudspeaker delays, normal subjects perceive a fused image originating from the side of the leading loudspeaker. Separate tests at loudspeaker delays ranging from 0 to 8 ms were presented to groups of young and elderly subjects. At 0 ms delay, young subjects perceived the fused image to be located halfway between the loudspeakers; at progressively longer delays, the image was perceived closer to the leading loudspeaker. Significant numbers of elderly subjects exhibited discrimination difficulties with delays below 0.7 ms.

Adult↗
PubMed1991

Sound localization and sensitivity to interaural time differences in human infants.

The role of interaural time differences in infants' sound localization was investigated. One experiment on free-field sound localization corroborated previous findings that the minimum audible angle changes substantially toward the end of the first half year after birth, and 3 experiments explored interaural time discrimination in that age range. The first of these 3 experiments used an adaptive psychophysical procedure, showing that infants responded appropriately in a sound lateralization task that provides a direct measure of interaural time discrimination. The other 2 experiments improved on the psychophysical procedure by taking into account the ceiling level on performance in the task. Infants aged 16, 20, and 28 weeks had thresholds in the range of 50 to 75 microsec, with no apparent age difference. These thresholds were much lower than would be predicted from studies of free-field sound localization, indicating that sensitivity to interaural time differences is not a limiting factor for the precision of sound localization in this age range. Instead, age-related changes in free-field sound localization may reflect the need to integrate across different localization cues and to calibrate the changing values of cues due to head growth.

Acoustic Stimulation↗
PubMed1975

Contribution of auditory cortex to sound localization in the monkey (Macaca mulatta).

Monkeys with lesions of auditory cortex were tested for their ability to localize the source of brief sounds. Although those deprived of primary auditory cortex bilaterally were able to indicate the direction of a sound with near-normal acuity, they were unable to locate its source. This dissociation of abilities suggest that the role of auditory cortex in sound localization is not so much sensory or perceptual as it is auditomotor or associative. Thus, sound localization joins loudness, pitch, and most other traditional attributes of sound as dimensions whose discrimination does not depend on auditory cortex. The question would now seem to turn to whether or not auditory cortex is necessary for any sensory discrimination whatever.

Acoustic Stimulation↗
PubMed1989

Vision calibrates sound localization in developing barn owls.

This study demonstrates that continuous exposure of baby barn owls to a displaced visual field causes a shift in sound localization in the direction of the visual displacement. This implies an innate dominance of vision over audition in the development and maintenance of sound localization. Twelve owls were raised from the first day of eye opening wearing binocular prisms that displaced the visual field to the right by 11 degrees, 23 degrees, or 34 degrees. The prisms were worn for periods of up to 7 months. Consistent with previous results (Knudsen and Knudsen, 1989a), owls reared with displacing prisms did not adjust head orientation to visual stimuli. While wearing prisms, owls consistently oriented the head to the right of visual targets, and, as soon as the prisms were removed, they oriented the head directly at visual targets, as do normal owls. In contrast, prism-reared owls did change head orientation to sound sources even though auditory cues were not altered significantly. Birds reared wearing 11 degrees or 23 degrees prisms oriented the head to the right of acoustic targets by an amount approximately equal to the optical displacement induced by the prisms. Birds raised wearing 34 degrees prisms adjusted sound localization by only about 50% of the optical displacement. Thus, visually guided adjustment of sound localization appears to be limited to about 20 degrees in azimuth. The data indicate that when confronted with consistently discordant localization information from the auditory and visual systems, developing owls use vision to calibrate associations of auditory localization cues with locations in space in an attempt to bring into alignment the perceived locations of auditory and visual stimuli emanating from a common source. Vision exerts this instructive influence on sound localization whether or not visual information is accurate.

Animals↗
PubMed1976

Role of neocortex in binaural hearing in the cat. II. The 'precedence effect' in sound localization.

The 'precedence effect' in sound localization refers to the situation in which two speakers, separated in space, emit identical sounds but one speaker leads by a few milliseconds. Normal observers perceive all the sound as originating from the leading speaker. In the present experiment cats were tested before and after unilateral ablation of auditory cortex on how well they could transfer a learned sound loclization response from situations involving unpaired sound sources to those with paired sources. Cats were tested with tone pairs separated by 5 msec and with clicks separated by delays of 3, 5, 7, 9, 12 and 16 msec. Preoperatively, the cats averaged 98% correct at a delay of 3 msec and 58% correct at 16 msec. Before surgery the probability of an error was independent of which speaker was leading; after surgery cats made significantly more errors when the leading speaker was located opposite the side of the lesion. Considerable individual variability was found with the 3 and 5 msec delay tests; some cats showed no evidence of a cortical deficit while others exhibited initial severe deficits which disappeared with training. At delays of 7-16 msec all cats showed severe directional deficits which were still present after 9 months of retraining. Results are interpreted as supporting the hypothesis that unilateral lesions disrupt binaural loudness rather than temporal relations.

Animals↗
PubMed1990

Tests of the precedence effect in sound localization reveal abnormalities in multiple sclerosis.

The precedence effect in sound localization involves presenting identical sounds (e.g., clicks) from pairs of matched speakers situated on opposite sides of a subject's head, with the clicks from one speaker preceding those from the other by a short interval. With appropriate delays, normal subjects perceive a fused image which originates from the side of the leading speaker. This test was administered to 24 patients with multiple sclerosis (MS). Separate tests involving speaker delays ranging from 0 msec (simultaneous presentation) to 8 msec were presented. At 0 msec delay, normal subjects perceived the fused image to be located halfway between the two speakers; at progressively longer delays, the image was perceived closer to the leading speaker. In contrast to normal subjects, a large proportion of the MS subjects exhibited difficulties with the task. The discrimination deficit was limited to delays below 1 msec, suggesting a problem involving an increased threshold for lateralizing the fused image away from midline toward the side of the leading speaker. The neural instability produced by demyelination in MS patients might account for this pattern of results.

Adult↗
PubMed1990

An evaluation of an in vivo local sound speed estimation technique by the crossed beam method.

An in vivo local sound speed estimation technique, using the crossed beam method, has been proposed and its applicability was evaluated. At first, the potential of this technique was studied by a mapping simulation using the ray tracing technique followed by an experiment with a cylindrical agar phantom. The simulation result showed that an exact measurement of local sound speed values was difficult, but the sound speed information for the local region (its relative magnitude to the surrounding medium) was emphasized as a refraction mapping pattern. The experimental results agreed well with the calculation results. Furthermore, a clinical application was performed, using the clinical system (modified electronic linear scanner), on two liver tumor patients.

Acoustics↗
PubMed1976

Sound localization in anurans. I. Evidence of binaural interaction in dorsal medullary nucleus of bullfrogs (Rana catesbeiana).

1. The response patterns of single cells to monaural and binaural acoustic stimuli were studied in the dorsal medullary nucleus of the bullfrog (Rana catesbeiana). This nucleus represents the first ascending center in the anuran's central auditory nervous system. 2. Of the 142 cells isolated, 75 units responded only to monaural stimulation. Approximately 80% of these monaural cells could be excited by the ipsilateral ear, while the remaining 20% received their excitatory input from the contralateral ear. The other 67 units responded to binaural stimuli. Of these binaural cells, 14 could be excited by either contralateral or ipsilateral stimuli, and the threshold and best excitatory frequency were similar for each ear (EE). The other 53 binaural cells (EI) could be excited by stimulation of one ear and inhibited by stimulation of the other ear; for almost all of these cells the contralateral ear was excitatory and the ipsilateral ear was inhibitory. The best inhibitory frequency for one ear was approximately the same as the best excitatory frequency for the other ear, and the threshold for inhibition was near the threshold for excitation. 3. The tuning curves for all of the cells in the dorsal medullary nucleus were unimodal with "Q" values ranging from 0.4 to 4. The excitatory thresholds were widely scattered between 22 and 115 dB SPL. 4. The distribution of best excitatory frequencies for the monaural cells comprised three groups: 200-300, 500-800, and 900-1,600 Hz. The best excitatory frequencies of the binaural cells were scattered over this entire range, with a broad peak around 200-800 Hz. 5. Approximately 80% of the cells in the dorsal nucleus responded tonically throughout the duration of an excitatory tone burst. The remaining 20% of the cells responded phasically during the transient stages of a tone burst over a wide intensity range. 6. Response latencies were compared for the two types of monaural cells to tones at their best exciatatory frequencies at 10 dB above threshold. The latencies for the contralaterally excitable cells were just a few milliseconds longer than the latencies for the ipsilaterally excitable cells. For binaural cells the latency for contralateral stimulation was only 1-2 ms longer than for ipsilateral stimulation. It was concluded that the contralateral input to the dorsal medullary nucleus is not of efferent descending origin from higher auditory centers. 7. All of the binaural EI cells were sensitive to small interaural intensity differences and many were also sensitive to minute interaural time differences. These cells likely play a role in localization of sounds of significance to anurans.

Action Potentials↗